Includes bibliographical references.Geminiviruses replicate via a rolling circle mechanism, which initiates at the origin of replication located within the long intergenic region (LIR). The viral replication associated-protein (Rep) in conjunction with the host's DNA replication machinery is responsible for the initiation and termination of the replication cycle from a stem-loop structure, located within the LIR and conserved throughout the three genera of Geminiviridae. The specific interaction between the Rep protein with sequences within the intergenic region has been well characterised for the begomoviruses and to some extent the curtoviruses; however, this interaction in the mastreviruses, and in particular maize streak virus (MSV), has yet to be fully explored. A theoretical model has been proposed based on sequence data and informed by the current understanding of replication specificity in begomoviruses. Due to the lack of conservation of the stem sequence of the stem-loop structure amongst mastreviruses, the model implicates a pair of nucleotide sequence repeats called iterons. These are located within the stem structure, and on the complementary sense side of the LIR. The former is the putative site of Rep interaction with the LIR. These iterons would therefore potentially act as the determinants of replication specificity amongst mastreviruses